Rate control method and apparatus for data packet transmission

Abstract

Base stations control the transmission rate that is used by UE (user equipment) to forward them information. A UE periodically forwards a rate request to a base station if the UE needs to have its data transmission rate to the base station increased or decreased, and the base station responds with a rate command. An error can occur in the transmission of the rate command, such that a rate Rnb transmitted by the base station and detected by the UE as Rue may not match. Various schemes are proposed for reducing and correcting such transmission errors. A first scheme involves periodically resetting the transmission rate of the base station and UE with a reference rate. Second to fourth schemes involve periodically comparing the transmission rates of the base station and UE, and replacing the rate of the UE if they differ. A fifth scheme involves a filtering of the feedback command in order to reduce the impact of error propagation. A sixth scheme, which may be used separately or in conjunction with any of the foregoing schemes, involves adjusting a power offset with a repetition factor. All of the schemes are modified during a soft handover of the UE from the base station to a new base station.

Description

TECHNICAL FIELD [0001] The present invention relates to data packet transmission rates, and more particularly, to a closed-loop rate control method and apparatus for data packet transmissions from a UE (user equipment) such as a mobile phone to a base station. BACKGROUND ART [0002] In cellular wireless systems, Wideband Code-Division Multiple-Access (W-CDMA, or the European equivalent UMTS (Universal Mobile Telecommunications System)) is the radio-access technology available worldwide providing high-speed wireless data packet service, i.e. wireless internet access and multimedia service, as well as conventional voice services. [0003] To enable more-efficient downlink data packet transmission, a closed-loop based rate control called High-Speed Downlink Packet Access (HSDPA) was adopted as the next UMTS release. HSDPA is based on a closed-loop rate-control scheme in which the downlink transmission data rate is changed as rapidly as channel variation by controlling rate-matching and mo...

AI Technical Summary

Benefits of technology

[0014] The subject invention seeks to reduce the error in signalling a maximum data transmission rate from a system node to user equipment (UE), while at the same time not requiring the amount of increased system overhead of the conventional system in attaining that objective.

Problems solved by technology

There are two sources of feedback errors: (1) an uplink error in UE rate request, and (2) a downlink feedback error in the rate control command of node B. Both types of errors are inevitable because of factors such as limitations in transmission power, severe fading in wireless channels, etc.

An uplink error incurs a slow adaptation of uplink rate control, while the latter breaks down the synchronization between Rnb and Rue.

Loss of such synchronization causes the mobile phone, i.e. the UE, to transmit the data packet with excessively-high or excessively-low transmission power.

With the former, there is a significant loss of manageability of uplink noise, while with the latter, the UE suffers low data throughput.

Firstly, a solution that only reduces the probability of random walking is not suitable in the case of lengthy radio communications.

Fourthly, it is desirable that there be no, or only minor, impact on the system's radio network controller (RNC), which controls essential communication between node B and the UE, since any involvement by the RNC necessitates additional expensive signalling between the RNC and node B, and also possibly between the RNC and the UE.

However, the spectral efficiency of this solution is lower than for the differentially-encoded bit stream due to the larger number of signalling bits per rate-control command.

A major difficulty with this solution is that the overhead is much higher than that involved with transmitting only a differential value.

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